CN110350398B

CN110350398B - Spark plug

Info

Publication number: CN110350398B
Application number: CN201910216599.5A
Authority: CN
Inventors: 岩崎喜知; 上垣裕则
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2018-04-03
Filing date: 2019-03-21
Publication date: 2021-04-02
Anticipated expiration: 2039-03-21
Also published as: JP6711857B2; US10777975B2; DE102019108338A1; US20190305523A1; JP2019185871A; CN110350398A

Abstract

The invention provides a spark plug, wherein a conductive sealing material is filled at the rear end side of a center electrode, and a gap between the center electrode and the conductive sealing material can be inhibited. In the spark plug, an insulator (3) is provided with a through hole (3A) in a form in which a first hole portion (11) and a second hole portion (12) are connected via a step portion (13), and the through hole extends in the direction of the axis. The center electrode (4) is provided with a flange portion (44) that is disposed in the second hole portion and supported by the stepped portion, and a shaft portion (42) that extends from the flange portion to the first hole portion side, and has a thermal expansion coefficient greater than that of the insulator. The conductive sealing material (61) has a thermal expansion coefficient smaller than that of the center electrode and is filled at least between the center electrode and the resistor (63) in the second hole. The center electrode has a recess portion continuous from the rear end of the center electrode toward the tip end side, and the recess portion is provided at least at the position of the maximum outer diameter portion (44B) of the flange portion in the axial direction.

Description

Spark plug

Technical Field

The present invention relates to a spark plug.

Background

Patent document 1 discloses an example of a spark plug. The spark plug disclosed in patent document 1 includes a cylindrical insulator, a center electrode held inside the insulator, a ground electrode forming a spark discharge gap with the center electrode, and a resistor held inside the insulator on the base end side of the center electrode. A conductive sealing material (glass sealing material) is filled between the resistor and the center electrode. In this spark plug, since the resistor is disposed inside the insulator, radio wave noise generated from the center electrode can be suppressed, and since the conductive sealing material (glass sealing material) is disposed in a state of being closely adhered to both sides of the resistor, it is possible to improve sealability in the insulator and secure a conductive path to the center electrode.

Patent document 1: japanese laid-open patent publication No. 9-266055

Disclosure of Invention

However, in such a spark plug, since the difference in thermal expansion coefficient between the insulator and the center electrode tends to increase, there is a possibility that a gap due to the difference in thermal expansion coefficient may be generated during the manufacturing process.

For example, when glass sealing is performed by using hot press molding, the following method can be employed: after the center electrode, the conductive sealing material (powder material as a raw material), the resistor, the terminal fittings, and the like are arranged in the through hole formed in the insulator, the powder material is melted by heating these components, and thereafter, the melted conductive sealing material is solidified and bonded between the center electrode and the resistor by cooling. However, as the difference in thermal expansion coefficient between the center electrode and the insulator increases, the degree of thermal contraction of the center electrode during cooling increases as compared with the insulator, and a gap tends to be formed near the boundary surface of the center electrode. The larger the proportion of the center electrode in the through hole, the more likely such an influence of the difference in thermal expansion occurs, and the more likely it occurs in the vicinity of the flange portion disposed on the rear end side of the center electrode.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a spark plug in which a conductive sealing material is filled in a rear end side of a center electrode, wherein a gap is prevented from being generated between the center electrode and the conductive sealing material, and adhesion between the center electrode and the conductive sealing material can be improved.

A spark plug according to one aspect of the present invention includes: a cylindrical main body metal member having a ground electrode connected to a tip end side of the main body metal member; an insulator including a through hole extending in an axial direction, the through hole being formed such that a first hole and a second hole having an inner diameter larger than that of the first hole are connected to each other via a stepped portion; a center electrode that is provided with a flange portion that is disposed in the second hole portion and supported by the step portion, and a shaft portion that extends from the flange portion toward the first hole portion, and that has a thermal expansion coefficient greater than that of the insulator; a resistor body disposed in the second hole portion, and a tip end of the resistor body itself being disposed apart from a rear end of the center electrode; and a conductive sealing material having a thermal expansion coefficient smaller than that of the center electrode, the conductive sealing material being filled at least between the center electrode and the resistor in the second hole, the center electrode having a concave portion continuous from a rear end side thereof toward a distal end side thereof, the concave portion being provided at least at a position of a maximum outer diameter portion of the flange portion in the axial direction, the conductive sealing material entering the concave portion from the rear end of the center electrode.

In the spark plug, the entire region inside the flange portion is not formed with the material of the center electrode at the position of the maximum outer diameter portion of the flange portion, and a partial region inside is formed with the conductive sealing material having a smaller thermal expansion coefficient than the center electrode. With this configuration, the thickness of the center electrode can be reduced at the maximum outer diameter portion of the flange portion, and thermal expansion and thermal contraction can be reduced over the entire maximum outer diameter portion. Therefore, the amount of expansion in the heating step and the amount of contraction in the cooling step can be reduced, and the occurrence of a gap in the vicinity of the maximum outer diameter portion due to the difference in thermal expansion between the insulator and the center electrode can be effectively suppressed. Further, in the above spark plug, the recessed portion is formed so as to reach the maximum outer diameter portion from the rear end of the center electrode in the axial direction, and the conductive sealing material is caused to enter the inside of the recessed portion, so that a larger area of contact between the conductive sealing material and the center electrode can be secured at the rear end side of the center electrode. Therefore, the adhesion between the conductive sealing material and the center electrode can be effectively improved.

In the spark plug of the present invention, a ratio α/β of an inner diameter α of the recess portion to an outer diameter β of the flange portion may be 40% or more at a position of a maximum outer diameter portion of the flange portion in the axial direction in a cross-sectional plane cut in an arbitrary plane direction of the axial line.

Accordingly, the ratio of the concave portion can be secured to be larger at the position of the maximum outer diameter portion of the flange portion, and therefore, the thickness of the center electrode at the maximum outer diameter portion can be further suppressed, and the expansion amount in the heating step and the contraction amount in the cooling step can be further reduced. Further, since α/β in the cross-section obtained by cutting in any plane direction of the axis is 40% or more, the thickness of the center electrode can be reduced in the entire circumferential direction, and the occurrence of a gap due to a difference in thermal expansion coefficient in the vicinity of the maximum outer diameter portion can be more reliably suppressed.

In the spark plug of the present invention, the stepped portion may have a tapered portion whose inner diameter gradually decreases as the stepped portion approaches the first hole portion. Further, a surface of the flange portion on the tip end side may be in contact with a surface of the tapered portion, and a tip end of the recess portion may be located on the first hole portion side with respect to the tip end of the tapered portion.

Accordingly, the thickness of the center electrode can be reduced at least in the range from the rear end of the center electrode to the tip end of the tapered portion in the axial direction, and the occurrence of a gap in this range can be suppressed. Further, since the depth (length in the axial direction) of the recessed portion becomes larger, the area of contact between the conductive sealing material and the center electrode can be made larger, and the adhesiveness between the conductive sealing material and the center electrode can be further improved.

In the spark plug of the present invention, the conductive sealing material may be interposed between the outer peripheral surface of the flange portion and the inner peripheral surface of the through hole. Further, the tip of the recess itself may be disposed closer to the ground electrode side in the axial direction than the tip of the portion of the conductive sealing material disposed outside the center electrode.

In this way, if the conductive sealing material enters between the outer peripheral surface of the flange portion and the inner peripheral surface of the through hole, the sealing property between the outer peripheral surface of the flange portion and the inner peripheral surface of the through hole is further improved. However, in this configuration, if the flange portion has a large thickness, the amount of expansion or contraction of the flange portion increases in the heating step or the cooling step, and therefore a gap is likely to be formed between the outer peripheral surface of the flange portion and the conductive sealing material. However, according to the present invention, the conductive sealing material is caused to enter the recess portion, whereby thermal expansion and thermal contraction can be suppressed over the entire flange portion, and therefore, the occurrence of a gap in the vicinity of the outer peripheral surface of the flange portion can be reliably suppressed. Further, since the depth (length in the axial direction) of the recessed portion becomes larger, the area of contact between the conductive sealing material and the center electrode can be made larger, and the adhesiveness between the conductive sealing material and the center electrode can be further improved.

In the spark plug of the present invention, the flange portion may have a reduced diameter portion whose outer diameter gradually decreases as the flange portion approaches the shaft portion, at a position closer to the tip end side than the maximum outer diameter portion. The recess may have a small diameter portion having an inner diameter smaller than the maximum inner diameter of the maximum outer diameter portion at a position closer to the shaft portion side than the rear end of the reduced diameter portion in the axial direction.

In the configuration in which the recessed portion is provided as in the present invention, by forming the recessed portion deeper, a larger region in the axial direction in which the difference in thermal expansion coefficient can be suppressed can be secured, and the adhesion between the conductive sealing material and the center electrode can be further improved. However, in the structure in which the reduced diameter portion (the portion whose outer diameter is gradually reduced as it approaches the shaft portion) is formed on the distal end side of the flange portion, if the concave portion having a large inner diameter is formed so as to reach the inside of the reduced diameter portion, the thickness of the reduced diameter portion may be reduced, and the strength may be insufficient. However, with the above-described configuration, if the small diameter portion (the portion having an inner diameter smaller than the maximum inner diameter at the maximum outer diameter portion) is provided in the recess portion on the shaft portion side of the rear end of the reduced diameter portion, the recess portion can be formed deeper while ensuring a larger wall thickness at the reduced diameter portion.

In the spark plug of the present invention, a diameter-enlarged portion whose inner diameter is gradually increased toward the rear end may be provided on the rear end side of the recess.

If the enlarged diameter portion is provided in this way, the raw material of the conductive sealing material is likely to enter the recessed portion in the manufacturing process, and therefore the density of the conductive sealing material in the recessed portion is likely to be increased.

According to the spark plug described above, which is one aspect of the present invention, it is possible to improve the adhesion between the center electrode and the conductive sealing material while suppressing the occurrence of a gap between the center electrode and the conductive sealing material.

Drawings

Fig. 1 is a schematic sectional view showing an example of a spark plug according to a first embodiment.

Fig. 2 is an enlarged cross-sectional view showing the vicinity of the rear end portion of the center electrode in the spark plug of the first embodiment.

Fig. 3 is an enlarged cross-sectional view showing the vicinity of the rear end portion of the center electrode in the spark plug of the second embodiment.

Fig. 4 is an enlarged cross-sectional view showing the vicinity of the rear end portion of the center electrode in the spark plug of modification 1.

Fig. 5 is an enlarged cross-sectional view showing the vicinity of the rear end portion of the center electrode in the spark plug of modification 2.

Fig. 6 is an enlarged cross-sectional view showing the vicinity of the rear end portion of the center electrode in the spark plug of modification 3.

Detailed Description

A. First embodiment

A1. Basic structure of spark plug

Fig. 1 is a schematic sectional view showing the overall structure of a spark plug 1 according to a first embodiment of the present invention. A line CL illustrated in fig. 1 shows a central axis of the spark plug 1. The cross section illustrated in fig. 1 is a cross section obtained by cutting along the center axis CL at the position of the center axis CL.

In the following description, the central axis CL is also referred to as "axis CL", and a direction parallel to the central axis CL is also referred to as "axial direction". The axial direction is defined as the front-rear direction, the side closer to the flashover portion (the spark discharge gap g side) in the axial direction is defined as the front side of the spark plug 1, and the side where the terminal fitting 5 protrudes in the axial direction is defined as the rear side. The side closer to the spark gap in the axial direction is referred to as the tip side of the spark plug 1, and the side opposite to the spark gap in the axial direction is referred to as the rear end side.

The spark plug 1 includes an insulator 3, a center electrode 4, a terminal fitting 5, a metal fitting 7, an electrical connection portion 60, and a ground electrode 8.

The metal shell 7 is a cylindrical (specifically, substantially cylindrical) member to which a ground electrode 8 is connected on the tip end side thereof, and is formed so as to receive and hold a part of the insulator 3. A screw portion 9 is formed on the outer peripheral surface of the body metal 7 in the distal direction, and the spark plug 1 is attached to a cylinder head of an internal combustion engine, not shown, by the screw portion 9.

The insulator 3 is held on the inner peripheral portion of the metallic body 7 with talc 10 and a filler 14 interposed therebetween, and is fixed to the metallic body 7 in a state where the vicinity of the tip end portion (tip end portion) protrudes from the tip end surface (tip end face) of the metallic body 7. The through hole 3A is a shaft hole formed to penetrate between a tip end portion (front end portion) and a rear end portion of the insulator 3, and extends in the direction of the axis CL. The through-hole 3A includes a first hole 11 for holding the center electrode 4 at the distal end side of the insulator 3 and a second hole 12 for accommodating the electrical connection portion 60 at the rear side of the first hole 11. The inner circumferential surfaces of the first hole 11 and the second hole 12 are both cylindrical surfaces centered on the axis CL, and the diameter (inner diameter) of the inner circumferential surface of the second hole 12 is larger than the diameter (inner diameter) of the inner circumferential surface of the first hole 11. A tapered step portion 13 is provided as a part of the through hole 3A between the first hole portion 11 and the second hole portion 12, and the step portion 13 expands in diameter toward the rear side so that the diameter of the inner peripheral surface increases toward the rear side. The first hole 11 has a constant inner diameter in a range from the tip (front end) of the step portion 13 to the tip (front end) of the insulator 3, and the second hole 12 has a constant inner diameter in a range from the rear end of the step portion 13 to a predetermined position on the rear side of the tip (front end) of the terminal fitting 5. In this way, the through hole 3A of the insulator 3 is in a form in which the first hole 11 and the second hole 12 having an inner diameter larger than that of the first hole 11 are connected via the stepped portion 13. The insulator 3 is preferably a material having mechanical strength, thermal strength, electrical strength, and the like, and examples of such a material include a ceramic sintered body mainly composed of alumina. The insulator 3 has a thermal expansion coefficient smaller than that of the center electrode 4 and smaller than those of the conductive sealing material 61 and the second sealing material 62.

The center electrode 4 is held at the tip end side (tip end side) of the through hole 3A, is partially exposed so as to protrude from the tip end surface of the insulator 3, and is held in a state of being insulated from the main metal fitting 7. The center electrode 4 is housed in the through hole 3A so that a flange portion 44 is formed on the rear end side, a shaft portion 42 having an outer diameter smaller than that of the flange portion 44 is connected to the front side of the flange portion 44, and a cylindrical portion 45 having an outer diameter smaller than that of the flange portion 44 is connected to the rear side of the flange portion 44. The flange portion 44 is supported by the step portion 13 so as to be disposed in the second hole portion 12 and locked to the step portion 13 of the through hole 3A. The cylindrical portion 45 is a portion extending rearward from the rear end of the flange portion 44, and is disposed in the second hole portion 12 together with the flange portion 44. The shaft portion 42 is a portion extending from the flange portion 44 toward the first hole portion 11, and is inserted into the first hole portion 11.

The center electrode 4 is preferably made of a material having thermal conductivity, mechanical strength, and the like, and is formed of a Ni-based alloy such as Inconel (trade name). The axial center portion of the center electrode 4 may be formed of a metal material having excellent thermal conductivity such as Cu or Ag. The thermal expansion coefficient of the center electrode 4 is larger than the thermal expansion coefficient of the insulator 3 and larger than the thermal expansion coefficients of the conductive sealing material 61 and the second sealing material 62.

The ground electrode 8 is formed such that one end thereof is joined to the tip end surface (front end surface) of the metal shell 7, and the tip end thereof is bent in a substantially L-shape in the middle thereof, and the tip end thereof faces the tip end (front end) of the center electrode 4 with a gap therebetween. The ground electrode 8 is formed of the same material as that of the center electrode 4.

Noble metal tips

29 and 30 made of platinum alloy, iridium alloy, or the like are provided on the surface of the center electrode 4 facing the ground electrode 8. A spark discharge gap g is formed between the

noble metal tips

29, 30. The noble metal tip of one or both of the center electrode 4 and the ground electrode 8 may be omitted.

The terminal fitting 5 is used to apply a voltage for spark discharge between the center electrode 4 and the ground electrode 8 to the center electrode 4 from the outside. The terminal fitting 5 is held at the other end side (rear end side) of the through hole 3A and is disposed so that a part thereof protrudes rearward from the rear end of the insulator 3. The surface of the distal end portion of the terminal fitting 5 has a concave-convex structure formed by, for example, embossing, thereby improving the close adhesion between the terminal fitting 5 and the second sealing member 62 and firmly fixing the terminal fitting 5 and the insulator 3. The terminal fitting 5 is formed of, for example, low carbon steel, and has a Ni metal layer formed on the surface thereof by plating or the like.

The electrical connection portion 60 is disposed between the center electrode 4 and the terminal fitting 5 inside the through hole 3A. The electrical connection portion 60 electrically connects the center electrode 4 and the terminal fitting 5 in the through hole 3A, and functions as a conduction path for conducting these. The electrical connection section 60 includes a resistor 63, a conductive sealing material 61, and a second sealing material 62.

The resistor 63 is a conductive portion that functions as a resistor between the terminal fitting 5 and the center electrode 4, and is disposed in the second hole 12 with its tip (front end) spaced apart from the rear end of the center electrode 4. The resistor 63 functions as a resistor, and suppresses generation of radio noise (noise) during spark discharge. The resistor 63 is made of a resistor material obtained by sintering a resistor composition containing glass powder and carbon-containing conductive powder.

The conductive sealing material 61 and the second sealing material 62 are layers for sealing the inside of the through hole 3A. The conductive sealing material 61 and the second sealing material 62 can be formed by sintering sealing powder containing glass powder such as sodium borosilicate glass and metal powder such as Cu and Fe. The thermal expansion coefficients of the conductive sealing material 61 and the second sealing material 62 are both smaller than the thermal expansion coefficient of the center electrode 4 and larger than the thermal expansion coefficient of the insulator 3.

The conductive sealing material 61 is a portion for sealing and fixing the insulator 3 and the center electrode 4 in the through hole 3A, and fills a space between the center electrode 4 and the resistor 63 in the second hole 12. The conductive sealing material 61 is disposed between the center electrode 4 and the resistor 63 in the through hole 3A so as to be closely adhered to the surface near the rear end of the center electrode 4 and to the distal end surface (distal end surface) of the resistor 63, electrically connects the center electrode 4 and the resistor 63, and functions as a conduction path between the center electrode 4 and the resistor 63.

The second sealing member 62 is a conductive sealing member for sealing and fixing the insulator 3 and the terminal fitting 5 in the through hole 3A, and is disposed between the terminal fitting 5 and the resistor 63 in the second hole 12. The second sealing member 62 is disposed between the terminal fitting 5 and the resistor 63 so as to be closely adhered to the rear end surface of the resistor 63 and to the surface in the vicinity of the distal end portion (the vicinity of the distal end portion) of the terminal fitting 5 in the second hole 12, electrically connects the terminal fitting 5 and the resistor 63, and functions as a conduction path between the terminal fitting 5 and the resistor 63.

A2. Detailed structure of the first embodiment

Next, the detailed configuration of the first embodiment will be described. Fig. 2 is an enlarged cross-sectional view showing the vicinity of the rear end portion of the center electrode in the spark plug 1 of the first embodiment.

In the example of fig. 2, the flange portion 44 of the center electrode 4 has a maximum outer diameter portion 44B and a reduced diameter portion 44A. The maximum outer diameter portion 44B is a portion of the flange portion 44 where the diameter of the outer peripheral surface is the largest, specifically, the outer peripheral surface is formed as a cylindrical surface, and is configured as an outer diameter constant portion having a constant outer diameter within a predetermined range (region AR1) in the axial direction. The reduced diameter portion 44A is arranged on the tip side of the maximum outer diameter portion 44B so as to be continuous from the tip (tip) of the maximum outer diameter portion 44B to the front side, and has a tapered shape in which the outer diameter gradually decreases as it approaches the shaft portion 42. In the example of fig. 2, the rear end of the reduced diameter portion 44A coincides with the tip (front end) of the maximum outer diameter portion 44B, and the tip (front end) of the reduced diameter portion 44A coincides with the rear end of the shaft portion 42.

In the example of fig. 2, the step portion 13 forming a part of the through hole 3A has a tapered portion 13A. Specifically, the stepped portion 13 is integrally formed as a tapered portion 13A, a rear end of the tapered portion 13A coincides with a tip (front end) of the second hole portion 12, and a tip (front end) of the tapered portion 13A coincides with a rear end of the first hole portion 11. The tapered portion 13A gradually decreases in inner diameter as it approaches the first hole 11, the inner diameter of the rear end of the tapered portion 13A matches the inner diameter of the second hole 12, and the inner diameter of the tip end of the tapered portion 13A matches the inner diameter of the first hole 11. The surface of the flange portion 44 on the tip side contacts the surface of the tapered portion 13A configured as described above. Specifically, the surface of the reduced diameter portion 44A of the flange portion 44 is configured to contact the surface of the tapered portion 13A.

The center electrode 4 has a recess 46 continuous from the rear end 4A of the center electrode 4 toward the distal end 4B (fig. 1) near the flange 44 configured as described above. The concave portion 46 is a hole portion formed in a shape recessed toward the front side along the axis line CL with the axis line CL as the center. The depth direction of the recess 46 is the axial direction (front-rear direction), and the deepest position of the recess 46 is the tip (front end) of the recess 46. Since the recessed portion 46 is formed in the above manner, in the center electrode 4, the shape of the region in which the recessed portion 46 is formed in the axial direction is a hollow shape (specifically, a substantially cylindrical shape).

As shown in fig. 2, the recess 46 is provided at the position of the maximum outer diameter portion 44B of the flange portion 44 at least in the axial direction. In fig. 2, a range in which the maximum outer diameter portion 44B is provided in the axial direction is indicated as a region AR1, and in the example of fig. 2, the recess 46 is formed over the entire range (region AR1) in which the maximum outer diameter portion 44B is provided. That is, the tip 46A (tip) of the recess 46 is located further toward the tip side (front side) than the tip (tip) of the maximum outer diameter portion 44B. Specifically, the tip 46A of the recess 46 is located closer to the first hole 11 side than the tip (tip) of the tapered portion 13A, and the recess 46 is provided so as to extend over the entire range of the tapered portion 13A in the axial direction.

The recess 46 has a cylindrical surface portion 48 whose inner peripheral surface is configured as a cylindrical surface around the axis CL, an enlarged diameter portion 49 formed on the rear side of the cylindrical surface portion 48, and a small diameter portion 47 formed on the front side of the cylindrical surface portion 48.

The cylindrical surface portion 48 is formed within a predetermined range in the axial direction, and has a constant inner diameter D1 within the predetermined range. The cylindrical surface portion 48 is formed so as to extend across the cylindrical portion 45 and the flange portion 44, and the tip (tip) of the cylindrical surface portion 48 is located at a position close to the tip (tip) of the maximum outer diameter portion 44B in the region AR1 in the axial direction. In fig. 2, the inner diameter of the cylindrical surface portion 48 (the maximum inner diameter of the recessed portion 46) is denoted by reference numeral D1, the outer diameter of the maximum outer diameter portion 44B (the maximum outer diameter of the flange portion 44) is denoted by reference numeral D2, and the inner diameter of the second hole portion 12 is denoted by reference numeral D3.

The diameter-enlarged portion 49 is formed on the rear end side of the recess 46, and is formed so that the inner diameter thereof gradually increases as it approaches the rear end of the recess 46. In the example of fig. 2, the rear end 4A of the center electrode 4 is the rear end of the enlarged diameter portion 49 and is also the rear end of the recess 46. The tip (front end) of the enlarged diameter portion 49 coincides with the rear end of the cylindrical surface portion 48, and the inner diameter of the tip (front end) of the enlarged diameter portion 49 coincides with the inner diameter D1 of the cylindrical surface portion 48. The inner peripheral surface of the enlarged diameter portion 49 is a tapered surface that gradually widens as it approaches the rear end of the recess 46.

The small diameter portion 47 has an inner diameter smaller than the inner diameter D1 of the cylindrical surface portion 48, and is formed such that the inner diameter gradually decreases as the tip (front end) of the recess 46 approaches. The inner diameter D1 of the cylindrical surface portion 48 is the maximum inner diameter at the maximum outer diameter portion 44B, and the inner diameter of the small diameter portion 47 is smaller than this maximum inner diameter. The rear end of the small diameter portion 47 is located at the same position as the rear end 44Z of the reduced diameter portion 44A in the axial direction or at a position slightly more to the rear side than the rear end of the reduced diameter portion 44A, and the tip (front end) of the small diameter portion 47 is located at a tip side (front side) than the tip 44Y (front end) of the reduced diameter portion 44A in the axial direction. In this way, at least a part of the small diameter portion 47 is provided on the shaft portion 42 side in the axial direction than the rear end 44Z of the reduced diameter portion 44A, specifically, over the entire range in which the reduced diameter portion 44A is provided in the axial direction. In the example of fig. 2, since the small diameter portion 47 is disposed so that the inner diameter thereof gradually decreases toward the distal end side (front side) over the entire range in which the reduced diameter portion 44A is provided in the axial direction, the thickness of the center electrode 4 can be easily ensured at the reduced diameter portion 44A.

The conductive sealing material 61 enters the recess 46 from the rear end of the center electrode 4, and fills the entire recess 46. Further, the conductive sealing material 61 is interposed between the outer peripheral surface of the center electrode 4 and the inner peripheral surface of the insulator 3 so as to surround a part of the rear end side of the center electrode 4 in the circumferential direction. Specifically, the conductive sealing material 61 is interposed between the outer peripheral surface of the cylindrical portion 45 and the inner peripheral surface of the insulator 3, and is disposed so as to surround the entire circumference of the cylindrical portion 45. Further, the conductive sealing material 61 is interposed between the outer peripheral surface of the maximum outer diameter portion 44B and the inner peripheral surface of the insulator 3, and is disposed so as to surround the entire circumference of the maximum outer diameter portion 44B. The tip 61A (tip) of the portion of the conductive sealing material 61 disposed outside the center electrode 4 is, for example, at the position of the tip (tip) of the maximum outer diameter portion 44B or at a position closer to the tip side (front side) than this position (for example, at a position between the diameter-reduced portion 44A and the tapered portion 13A). The recess 46 is disposed such that the tip 46A thereof is closer to the tip side (ground electrode 8 side) than the tip 61A in the axial direction.

In the spark plug 1 configured as described above, in a cross-sectional plane cut in an arbitrary plane direction of the axis CL, a ratio α/β of the inner diameter α of the recess 46 to the outer diameter β of the flange portion 44 is 40% or more at a position of the maximum outer diameter portion 44B of the flange portion 44 in the axis direction (a position of the region AR1 shown in fig. 2). Specifically, in an arbitrary virtual plane that is orthogonal to the axis line CL and passes through the maximum outer diameter portion 44B, the relationship "the ratio α/β of the inner diameter α of the concave portion 46 to the outer diameter β of the flange portion 44 in a cross-sectional plane that is cut in an arbitrary plane direction passing through the axis line CL is 40% or more" may be sufficient. For example, in an arbitrary virtual plane P1 perpendicular to the axis line CL in the predetermined region AR1, the relationship "the ratio α/β of the inner diameter α of the concave portion 46 to the outer diameter β of the flange portion 44 in a cross-sectional plane cut in an arbitrary plane direction passing through the axis line CL" may be 40% or more. More preferably, in an arbitrary imaginary plane passing through the maximum outer diameter portion 44B among imaginary planes orthogonal to the axis line CL, "a ratio α/β of the inner diameter α of the concave portion 46 to the outer diameter β of the flange portion 44 in each cross-sectional plane in all plane directions passing through the axis line CL" may be a relationship of 40% or more ".

As a method of determining whether or not such a relationship is obtained, it is sufficient to determine the position of the maximum outer diameter portion 44B in the spark plug 1 by a CT (computed tomography) technique, cut and polish the spark plug in a planar direction orthogonal to the axis line CL at the position, and confirm the cut surface by a Scanning Electron Microscope (SEM), and to confirm whether or not the ratio α/β of the inner diameter α of the concave portion 46 to the outer diameter β of the flange portion 44 in any direction passing through and orthogonal to the axis line CL in the cut surface is 40% or more.

In any imaginary plane passing through the portion (specifically, the cylindrical portion 45) closer to the rear end side than the maximum outer diameter portion 44B of the center electrode 4 in the imaginary plane orthogonal to the axis CL, "the ratio α/β of the inner diameter α of the concave portion 46 to the outer diameter β of the flange portion 44 in each cross-sectional plane passing through all the plane directions of the axis CL may be 40% or more.

A3. Second mode

Next, the spark plug 201 of the second embodiment will be described with reference to fig. 3 and the like. The spark plug 201 of the second embodiment is the same as the spark plug 1 of the first embodiment except that the structure of the region Z of the spark plug 1 of the first embodiment shown in fig. 2 (the region from the tip (front end) of the resistor 63 to the vicinity of the tip (front end) of the step portion 13 in the region of the through hole 3A) is replaced with the structure of the region Z shown in fig. 3. Specifically, the spark plug 201 of the second embodiment is different from the spark plug 1 of the first embodiment in the configuration of the center electrode and the conductive sealing material, and is the same as the spark plug 1 of the first embodiment except for the configuration of the center electrode and the conductive sealing material. Therefore, the same reference numerals as those of the spark plug 1 of the first embodiment are given to the spark plug 201 except for the center electrode and the conductive sealing material, and detailed description thereof is omitted.

The center electrode 204 of the spark plug 201 of the second embodiment has the same configuration as the center electrode 4 of the spark plug 1 of the first embodiment, except that the recess 46 shown in fig. 2 is replaced with the recess 246 shown in fig. 3. Therefore, the same reference numerals as those of the central electrode 4 are given to the same portions of the central electrode 204 as those of the central electrode 4 (fig. 2), and detailed descriptions thereof are omitted.

In the example of fig. 3, the concave portion 246 is also formed so as to be recessed from the rear end of the center electrode 204 toward the tip end side (front side), and is provided at least at the position of the maximum outer diameter portion 44B of the flange portion 44 in the axial direction. In fig. 3, a range in which the maximum outer diameter portion 44B is provided in the axial direction is shown as a region AR1, and the recess 246 is provided over the entire or almost entire range (region AR1) in which the maximum outer diameter portion 44B is provided. The tip 246A (tip) of the recess 246 may be located at the same position as the tip (tip) of the maximum outer diameter portion 44B in the axial direction, may be located on the tip side (front side) of the tip (tip) of the maximum outer diameter portion 44B, or may be located on the rear side of the tip (tip) of the maximum outer diameter portion 44B. The entire recess 246 is a cylindrical surface portion 248 having an inner peripheral surface formed as a cylindrical surface around the axis CL. The cylindrical surface portion 248 has a constant inner diameter D1 over the entire range from the rear end 246B to the tip end 246A in the axial direction. In such a configuration, the conductive sealing material 61 can be inserted into the concave portion 246, and the conductive sealing material 61 can be filled into the center electrode 4 while reducing the thickness of the center electrode at least at the position of the maximum outer diameter portion 44B.

A4. Effect

As shown in fig. 2, in the spark plug 1 of the first embodiment, the entire region inside the flange portion 44 is not formed with the material of the center electrode 4 at the position of the maximum outer diameter portion 44B of the flange portion 44, but a partial region inside is formed with the conductive sealing material 61 having a smaller thermal expansion coefficient than the center electrode 4. With this configuration, the thickness of the center electrode 4 can be suppressed at the maximum outer diameter portion 44B of the flange portion 44, and thermal expansion and thermal contraction can be suppressed at the position of the maximum outer diameter portion 44B. Therefore, when manufacturing the spark plug 1, the amount of expansion in the heating step and the amount of contraction in the cooling step can be reduced at the position of the maximum outer diameter portion 44B, and the occurrence of a gap in the vicinity of the maximum outer diameter portion 44B due to the difference in thermal expansion coefficient between the insulator 3 and the center electrode 4 can be effectively suppressed. If a gap is formed in the vicinity of the maximum outer diameter portion 44B, cracks and the like may easily occur from the gap as a starting point, and airtightness and adhesiveness may be impaired, but such a problem can be made less likely to occur with the configuration of fig. 2. Further, in the spark plug 1, the recessed portion 46 is formed so as to reach the maximum outer diameter portion 44B from the rear end of the center electrode 4 in the axial direction, and the conductive sealing material 61 is caused to enter the inside of the recessed portion 46, so that a larger area of contact between the conductive sealing material 61 and the center electrode 4 can be secured at the rear end side of the center electrode 4. Therefore, the adhesion between the conductive sealing material 61 and the center electrode 4 can be effectively improved. In addition, the same effect is obtained also in the spark plug 201 of the second embodiment shown in fig. 3.

As shown in fig. 2, in the spark plug 1 of the first aspect, in a cross-sectional plane cut in an arbitrary plane direction of the axis, a ratio α/β of an inner diameter α of the recess 46 to an outer diameter β of the flange 44 is 40% or more at a position of a maximum outer diameter portion 44B of the flange 44 in the axis direction. Accordingly, the ratio of the concave portion 46 can be secured to be larger at the position of the maximum outer diameter portion 44B, and therefore, the thickness of the center electrode 4 at the maximum outer diameter portion 44B can be further suppressed, and the expansion amount in the heating step and the contraction amount in the cooling step can be further reduced. Further, since each of α/β in the cross-sectional plane obtained by cutting in any plane direction of the axis is 40% or more, the thickness of the center electrode 4 can be reduced in the entire circumferential direction, and the occurrence of a gap due to a difference in thermal expansion coefficient in the vicinity of the maximum outer diameter portion 44B can be more reliably suppressed. The spark plug 201 of the second embodiment shown in fig. 3 also has the same configuration, and achieves the same effects.

In the spark plug 1 of the first embodiment shown in fig. 2, the stepped portion 13 has a tapered portion 13A whose inner diameter gradually decreases as it approaches the first hole portion 11. The surface of the flange 44 on the tip side contacts the surface of the tapered portion 13A, and the tip of the recess 46 is closer to the first hole 11 side than the tip of the tapered portion 13A. Accordingly, the thickness of the center electrode 4 can be reduced at least in the range from the rear end of the center electrode 4 to the tip end of the tapered portion 13A in the axial direction, and the occurrence of a gap in this range can be suppressed. Further, since the depth (length in the axial direction) of the recessed portion 46 becomes larger, the area of contact between the conductive sealing material 61 and the center electrode 4 can be made larger, and the adhesiveness between the conductive sealing material 61 and the center electrode 4 can be further improved.

In the spark plug 1 of the first embodiment shown in fig. 2, the conductive sealing material 61 enters between the outer peripheral surface of the flange portion 44 and the inner peripheral surface of the through hole 3A. The recess 46 is disposed such that the tip 46A thereof is located on the tip side (the ground electrode 8 side) in the axial direction with respect to the tip 61A of the portion of the conductive seal material 61 disposed outside the center electrode 4. In this way, if the conductive sealing material 61 enters between the outer peripheral surface of the flange portion 44 and the inner peripheral surface of the through-hole 3A, the sealing performance between the outer peripheral surface of the flange portion 44 and the inner peripheral surface of the through-hole 3A is further improved. However, in this configuration, if the flange portion 44 has a large thickness, the expansion amount and the contraction amount of the flange portion 44 increase in the heating step and the cooling step, and therefore a gap is likely to be generated between the outer peripheral surface of the flange portion 44 and the conductive sealing material 61. However, according to the configuration of fig. 2, the conductive sealing material 61 is inserted into the recess 46, so that thermal expansion and thermal contraction can be suppressed over the entire flange portion 44, and the occurrence of a gap in the vicinity of the outer peripheral surface of the flange portion 44 can be reliably suppressed. Further, since the depth (length in the axial direction) of the recessed portion 46 is so large that the tip 46A thereof reaches the tip side of the tip 61A of the conductive sealing material 61, the area of contact between the conductive sealing material 61 and the center electrode 4 can be made larger, and the adhesiveness between the conductive sealing material 61 and the center electrode 4 can be further improved.

In the spark plug 1 of the first embodiment shown in fig. 2, the flange portion 44 has a reduced diameter portion 44A whose outer diameter gradually decreases toward the shaft portion 42 at a position closer to the tip end side than the maximum outer diameter portion 44B. The recess 46 has a small diameter portion 47 having an inner diameter smaller than the maximum inner diameter (inner diameter D1) of the maximum outer diameter portion 44B at a position closer to the shaft portion 42 than the rear end of the reduced diameter portion 44A in the axial direction. In the structure in which the recess 46 is provided as in the spark plug 1, the recess 46 is formed deeper, so that a larger region in which the difference in thermal expansion coefficient can be suppressed can be secured in the axial direction, and the adhesion between the conductive sealing material 61 and the center electrode 4 can be further improved, but in the structure in which the reduced diameter portion 44A (the portion in which the outer diameter is gradually reduced as the portion approaches the shaft portion 42) is formed on the tip end side of the flange portion 44, if the recess 46 having a large inner diameter is formed so as to reach the inside of the reduced diameter portion 44A, the thickness at the reduced diameter portion 44A becomes small, and there is a possibility that the strength is insufficient. However, as shown in fig. 2, if the small diameter portion 47 (the portion having an inner diameter smaller than the maximum inner diameter at the maximum outer diameter portion 44B) is provided in the recess portion 46 on the shaft portion 42 side with respect to the rear end of the reduced diameter portion 44A, the recess portion 46 can be formed deeper while ensuring a larger wall thickness at the reduced diameter portion 44A.

In the spark plug 1 of the first embodiment shown in fig. 2, a diameter-enlarged portion 49 whose inner diameter gradually increases as it approaches the rear end is provided on the rear end side of the recess 46. If the diameter-enlarged portion 49 is provided in this way, the raw material of the conductive sealing material 61 is likely to enter the concave portion 46 in the manufacturing process, and therefore the density of the conductive sealing material 61 in the concave portion 46 is likely to be increased. For example, in the case of glass sealing by hot press molding, the following method can be employed: after the center electrode, the conductive sealing material (powder material as a raw material), the resistor, the terminal fittings, and the like are arranged in the through hole formed in the insulator, the powder material is melted by heating these components, and thereafter, the melted conductive sealing material is solidified and bonded between the center electrode and the resistor by cooling. In the case of manufacturing by such a process, if the raw material of the conductive sealing material 61 is less likely to enter the concave portion 46 in the molded body to be the center electrode 4, the density of the conductive sealing material 61 in the concave portion 46 in the final product may decrease, and cracking or the like may occur in the vicinity of the concave portion 46 when used, but if the diameter-enlarged portion 49 having the configuration shown in fig. 2 is provided, such a problem may be less likely to occur.

A5. Evaluation test

Next, the results of tests performed to verify the effects of the present invention will be described.

As examples 1 to 18 for the verification test, 18 kinds of spark plugs were prepared. The 18 kinds of spark plugs have the same structure as the spark plug 201 of the second embodiment shown in fig. 3.

Examples 1 to 18 were obtained by variously changing the inner diameter D1, the outer diameter D2 and the inner diameter D3 shown in FIG. 3. The spark plugs of examples 1 to 6 were identical except that the inner diameters D1 (inner diameters of the concave portions 246) shown in fig. 3 were different from each other. The spark plugs of examples 7 to 18 were different from those of examples 1 to 6 in the magnitude of the outer diameter D2 (the outer diameter of the maximum outer diameter portion 44B of the flange portion 44) shown in fig. 3. The spark plugs of examples 7 to 12 were identical except that the inner diameters D1 (inner diameters of the concave portions 246) shown in fig. 3 were different from each other. The spark plugs of examples 13 to 18 were different from those of examples 1 to 12 in an inner diameter D3 (inner diameter of the second hole 12) shown in fig. 3. The spark plugs of examples 13 to 18 were identical except that the inner diameters D1 (inner diameters of the concave portions 246) shown in fig. 3 were different from each other.

In the configurations of examples 1 to 18, the inner peripheral surface of the concave portion 246 shown in fig. 3 is a cylindrical surface (cylindrical surface of the inner diameter D1) centered on the axis CL, the outer peripheral surface of the maximum outer diameter portion 44B is a cylindrical surface (cylindrical surface of the outer diameter D2) centered on the axis CL, and the inner peripheral surface of the second hole portion 12 is also a cylindrical surface (cylindrical surface of the inner diameter D3) centered on the axis CL. In each of examples 1 to 18 configured as described above, in any imaginary plane that is orthogonal to the axis CL and passes through the maximum outer diameter portion 44B, the ratio α/β (D1/D2) of the inner diameter α (inner diameter D1) of the recess portion 46 to the outer diameter β (outer diameter D2 of the maximum outer diameter portion 44B) of the flange portion 44 in each cross-sectional plane in all plane directions passing through the axis CL is constant.

In addition, comparative examples 1 and 2 for comparison with examples were prepared. In comparative examples 1 and 2, a part of the spark plug 201 shown in fig. 3 was modified, and specifically, in the structure of fig. 3, the inside of the concave portion 246 was replaced with the material of the center electrode 204, and the concave portion 246 was not provided.

The examples 1 to 18 and comparative examples 1 and 2 were subjected to the evaluation test of the sealing property as follows. First, in a state where a resin having fluidity is contained in a predetermined container, a part of the tip end side of the spark plug (the vicinity of the tip end of the insulator 3 in fig. 1) as a sample is caused to enter the resin, and in a state where the vicinity of the tip end of the insulator is caused to enter the resin in this manner, a space in which the spark plug is arranged (a space outside the resin) is brought into a decompressed state. As the resin, epoxy resin (specialics-20, made by STRUERS (Styler) was used).

Specifically, three samples were prepared for each of examples 1 to 18 and comparative examples 1 and 2 shown in fig. 3. The above tests were performed for the respective samples, however, in the respective examples, one sample was tested in a reduced pressure state of 10000Pa, one sample was tested in a reduced pressure state of 5000Pa, and one sample was tested in a reduced pressure state of 1000 Pa.

Then, each sample after the test was polished to form a half-section cut in a plane direction perpendicular to the axis line CL at the tip position (tip position) of the maximum outer diameter portion 44B shown in FIG. 3, and whether or not the resin was present in the cross-section at the tip position (tip position) of the maximum outer diameter portion 44B was confirmed by an Energy Dispersive X-ray analyzer (EDS) attached to a Scanning Electron Microscope (SEM).

In examples 1 to 18 and comparative examples 1 and 2, the sample in which the resin could be confirmed in the sample tested under the reduced pressure of 10000Pa was "Δ", the sample in which the resin could be confirmed in the sample tested under the reduced pressure of 5000Pa was "o", the sample in which the resin could be confirmed in the sample tested under the reduced pressure of 1000Pa was "x", and the sample in which the resin could be confirmed in the sample tested under the reduced pressure of 1000Pa was "y". The results are shown in table 1.

[ TABLE 1 ]

As is apparent from table 1, in comparative examples 1 and 2 in which the concave portion 246 shown in fig. 3 was not present, resin was confirmed even in the sample tested in the reduced pressure state of 10000Pa, and in examples 1 to 18 in which the concave portion 246 was present, resin was not confirmed in the sample tested in the reduced pressure state of 10000 Pa. The reason for this is considered to be that in the samples of examples 1 to 18, the influence of the difference in thermal expansion coefficient between the center electrode 204 and the insulator 3 in the vicinity of the maximum outer diameter portion 44B is reduced by filling the concave portion 246 shown in fig. 3 with the conductive sealing material 61, and a gap is less likely to occur at the boundary surface of the maximum outer diameter portion 44B.

As is clear from Table 1, in examples 4 to 6, 9 to 12, and 15 to 18 in which the ratio of D1/D2 (. alpha./. beta.) was 40% or more, no resin was observed even under a reduced pressure of 5000 Pa. The reason for this is considered to be that the ratio of the conductive sealing material 61 is large at the position of the maximum outer diameter portion 44B shown in fig. 3, and therefore the influence of the difference in thermal expansion coefficient between the center electrode 204 and the insulator 3 in the vicinity of the maximum outer diameter portion 44B is further reduced, and the gap is further less likely to occur at the boundary surface of the maximum outer diameter portion 44B.

< other embodiments >

The present invention is not limited to the embodiments and modifications of the embodiments described herein, and can be realized in various configurations without departing from the spirit and scope thereof. For example, in order to solve a part or all of the above-described problems or to achieve a part or all of the above-described effects, technical features in the embodiments, examples, and modifications corresponding to technical features in the respective aspects described in the section of the summary of the invention may be appropriately replaced or combined. As long as this technical feature is not described as essential in the present specification, it can be deleted as appropriate. As a modification, for example, the following configuration is adopted.

In the above-described embodiment, the tip (tip) of the recess is located on the tip side (front side) in the axial direction with respect to the center position of the region (region AR1 shown in fig. 2 and 3) where the maximum outer diameter portion is provided, but in the above-described embodiment or any example obtained by modifying the above-described embodiment, the tip (tip) of the recess may be located on the rear side in the axial direction with respect to the center position of the region (region AR1 shown in fig. 2 and 3) where the maximum outer diameter portion is provided.

In the above-described embodiment or any example in which the above-described embodiment is modified, the recess is formed in the entire range of the maximum outer diameter portion (region AR1), but the recess may be provided in at least a part of the range of the maximum outer diameter portion in the axial direction.

The inner diameter of the cylindrical surface portion in the recess is not limited to the size shown in fig. 2 and 3, and may be larger or smaller.

In the configuration of the first embodiment shown in fig. 2, the diameter-enlarged portion may be omitted and the cylindrical surface portion may reach the rear end of the center electrode, or in the configuration of the first embodiment shown in fig. 2, the small diameter portion may be omitted and the distal end (front end) of the cylindrical surface portion may be positioned at the distal end (front end) of the recess.

In the above-described embodiment or any example modified from the above-described embodiment, the tip (tip) of the concave portion may be positioned at least on the tip side (front side) of the rear end of the maximum outer diameter portion in the axial direction, may be positioned on the tip side (front side) or on the rear side of the tip (tip) of the maximum outer diameter portion B, or may be positioned on the tip side (front side) or on the rear side of the tip (tip) of the reduced diameter portion.

In the above-described embodiment or any example obtained by modifying the above-described embodiment, the structure can be modified as shown in fig. 4 to 6. The spark plugs 301, 401, and 501 shown in fig. 4 to 6 are the same as the spark plug 1 of the first embodiment except that the structure of the region Z of the spark plug 1 of the first embodiment shown in fig. 2 (the region from the tip (front end) of the resistor 63 to the vicinity of the tip (front end) of the step portion 13 in the region in the through hole 3A) is replaced with the structure of the region Z shown in each of fig. 4 to 6. The spark plugs 301, 401, and 501 in fig. 4 to 6 are different from the spark plug 1 of the first embodiment in the structure of the center electrode and the conductive sealing material, and are the same as the spark plug 1 of the first embodiment except for the structure of the center electrode and the conductive sealing material. Therefore, the same reference numerals as those of the spark plug 1 of the first embodiment are given to the spark plugs 301, 401, and 501 except for the center electrode and the conductive sealing material, and detailed description thereof is omitted.

In the spark plug 301 according to modification 1 shown in fig. 4, the cylindrical portion is not provided on the rear side of the flange portion 44 at the center electrode 304, and the rear end of the flange portion 44 is the rear end of the center electrode 304. In the spark plug having such a configuration, a recess 346 is formed continuously from the rear end of the flange portion 44 toward the tip end side (front side). In this example, a cylindrical surface portion 348 having a constant inner diameter is formed within a predetermined range from the rear end of the flange portion 44, and a small diameter portion 347 is formed on the tip end side (front side) of the cylindrical surface portion 348. In the spark plug having such a configuration, the recess 346 is filled with the conductive sealing material 61.

In the spark plug 501 of modification 2 shown in fig. 5, the vicinity of the rear end portion of the center electrode 404 (the portion disposed on the rear side of the flange portion 44) is configured as a non-cylindrical portion and is formed so as to protrude on the rear side. The recess 446 is formed in a shape recessed toward the distal end side (front side) from a position slightly forward of the rear end of the center electrode 404, and a cylindrical surface portion 448 having a constant inner diameter is formed within a predetermined range from the rear end of the flange portion 44, and a small diameter portion 447 is formed at a position closer to the distal end side (front side) than the cylindrical surface portion 448. In the spark plug having such a structure, the recess 446 is filled with the conductive sealing material 61.

In the spark plug 501 of modification 3 shown in fig. 6, the cylindrical portion is not provided on the rear side of the flange portion 44 at the center electrode 504, and the rear end of the flange portion 44 is the rear end of the center electrode 504. In the spark plug having such a configuration, a recess 546 is formed continuously from the rear end of the flange portion 44 toward the tip end side (front side). In this example, an enlarged diameter portion 549 is formed in a predetermined range from the rear end of the flange portion 44, and a cylindrical surface portion 548 having a constant inner diameter is formed on the tip end side (front side) of the enlarged diameter portion 549. In the spark plug having such a structure, the conductive sealing material 61 is filled in the concave portion 546.

Description of the reference numerals

1. 201, 301, 401, 501 … spark plug

3 … insulator

3A … through hole

4. 204, 304, 404, 504 … center electrode

5 … terminal fitting

7 … main body metal piece

8 … ground electrode

11 … first hole part

12 … second aperture part

13 … step part

13A … taper

42 … shaft part

44 … flange portion

44A … reduced diameter part

44B … maximum outer diameter part

46. 246, 346, 446, 546 … recess

47. 347, 447 … small diameter section

49. 549 … expanding part

61 … first sealing layer (conductive sealing material)

63 … resistor body

CL … axis.

Claims

1. A spark plug is provided with:

a cylindrical main body metal member having a ground electrode connected to a tip end side of the main body metal member;

an insulator including a through hole extending in an axial direction, the through hole being formed such that a first hole and a second hole having an inner diameter larger than that of the first hole are connected to each other via a stepped portion;

a center electrode that is provided with a flange portion that is disposed in the second hole portion and supported by the step portion, and a shaft portion that extends from the flange portion toward the first hole portion, and that has a thermal expansion coefficient greater than that of the insulator;

a resistor body disposed in the second hole portion, and a tip end of the resistor body itself being disposed apart from a rear end of the center electrode; and

a conductive sealing material having a thermal expansion coefficient smaller than that of the center electrode and filled at least between the center electrode and the resistor in the second hole,

the center electrode has a recess continuous from a rear end side toward a tip end side thereof,

the recess portion is provided at least at a position of a maximum outer diameter portion of the flange portion in the direction of the axis,

the maximum outer diameter portion of the flange portion is smaller than the inner diameter of the second hole portion,

the conductive sealing material enters the recess from the rear end of the center electrode and enters between the outer peripheral surface of the center electrode and the inner peripheral surface of the insulator so as to circumferentially surround a part of the rear end side of the center electrode.

2. The spark plug of claim 1,

in a cross-section obtained by cutting in an arbitrary plane direction of the axis, a ratio α/β of an inner diameter α of the recess portion to an outer diameter β of the flange portion is 40% or more at a position of a maximum outer diameter portion of the flange portion in the direction of the axis.

3. The spark plug of claim 1,

the stepped portion has a tapered portion having an inner diameter gradually reduced as it approaches the first hole portion,

the surface of the tip side of the flange portion is in contact with the surface of the tapered portion,

the tip of the recess is closer to the first hole portion side than the tip of the tapered portion.

4. The spark plug of claim 1,

the conductive sealing material enters between the outer peripheral surface of the flange portion and the inner peripheral surface of the through hole,

the tip of the concave portion itself is disposed closer to the ground electrode side in the direction of the axis than the tip of the portion of the conductive sealing material disposed outside the center electrode.

5. The spark plug of claim 1,

the flange portion has a reduced diameter portion having an outer diameter gradually reduced toward the shaft portion at a position closer to the tip end side than the maximum outer diameter portion,

the recess has a small diameter portion having an inner diameter smaller than a maximum inner diameter of the maximum outer diameter portion at a position closer to the shaft portion side than a rear end of the reduced diameter portion in the axial direction.

6. The spark plug of claim 1,

an enlarged diameter portion having an inner diameter gradually increasing toward the rear end is provided on the rear end side of the recess.